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Feb 19, 2007, 11:00 AM
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Ralph B's Avatar
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Solar Micro Mite


I recently obtained a pair of high output solar cells from Spectrolab for a micro solar model. The cells are the same size as those I used on the Sol-Mite however these new cells are rated at nearly double the efficiency (31%). I decided that the light weight version of the Micro Mite that I had been flying indoors would be a good subject for a solar conversion. With the solar cells the weight of the Micro Mite was going to be increased to 9.5 grams. I was not sure if the 4MM drive would handle that much weight so I tested the model on a 20 MAH Full River cell with enough ballast to bring it up to 9.5 grams. I replaced the Microinvent 3222 prop with the Carbon Butterfly prop which has a little more blade area and pitch. The test was a huge success so I went ahead with the conversion. First flights were made yesterday. This "quarter scale" Sol-Mite has a much better power to weight ratio than the large one. It can fly in less than the perfect conditions that the larger model required. Specifications as follows:
Wing span: 8 inches
Flying weight: 9.5 grams
Equipment: Plantraco .38 gram, 3 channel receiver with a pair of Nick Leichty's remote actuators on rudder and elevator.
Drive: Didel MK04-10 motor with 7.1 to 1 ratio watch gears.
Prop: Carbon Butterfly

Ralph B
Last edited by Ralph B; Feb 19, 2007 at 11:10 AM.
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Feb 19, 2007, 11:09 AM
in pursuit of low wing loading
Gordon Johnson's Avatar
Ralph,
Wow that's great. You just keep making progress on the solar powered plane front.

Gordon
Feb 19, 2007, 11:39 AM
B A bay B E be B I bicky bi
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nice work, Ralph. i honestly didnt think i'd see something like this for a while yet. its good to see solar cells are getting that much better - 31% is quite a step up. amazing that the 4mm can haul around nearly 10 grams of weight. whats the weight of a single solar cell?

very cool

nick
Feb 19, 2007, 12:13 PM
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Ralph B's Avatar
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The cells weigh 1.9 grams each. I was really suprised that the 4MM drive was able to fly it. I expected to have to struggle to get enough thrust but the 7.1 ratio with the Carbon Butterfly prop flies it with authority. The flights yesterday were short because the wind kept tipping the wing up so the exposure to the sun was interupted which caused the receiver to "brown out". The sun here is lower at this time of year so I expect it will do much better with a better exposure angle.

Ralph
Feb 19, 2007, 12:24 PM
High-power Rocket Gliders
iter's Avatar
Very very impressive!

Re the receiver browning out. Plantracos take a loooong time to boot--usually enough time for a model to land before control can be reestablished after a momentary disconnect. Perhaps you could try a different RX, maybe one of Nick's, or one with YAPP? I wonder also how much a capacitor would weigh that could smooth out these "wing-tipping eclipses."

Ari.
Feb 19, 2007, 12:42 PM
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Ari:
You are exactly right. If necessary I will replace the receiver with one of Nick's. The sun at it's highest point yesterday was still somewhat low. The real exciting news for me is that in spite of the sun angle yesterday that it flew at all. I'm sure when we start getting the exposure angles that are typical here that there won't be any more brown outs. The larger Sol-Mite would not have been able to fly at all yesderday.

Ralph
Feb 19, 2007, 02:42 PM
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Sonic1's Avatar
Quote:
Originally Posted by iter
I wonder also how much a capacitor would weigh that could smooth out these "wing-tipping eclipses."

Ari.
Maybe one of these super capacitors might work....
Feb 19, 2007, 03:04 PM
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superb!..
Feb 19, 2007, 03:43 PM
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Wow Ralph, that's incredible!

Funny, yesterday, a guy was asking me about using solar cells on model planes. I explained to him how it required lots of wing area and how the cells were heavy, etc... So here you go and do this.

Very, very cool.

I assume the cells are very expensive?

Mark
Feb 19, 2007, 03:58 PM
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Mark:

The cells are not cheap, however, since I was only needing two cells they offered to send me a couple of samples. I do have some history with them (Sol-Mite) and I think they were interested in what I wanted to do. I really don't know what the cells would have cost but I did have to pay for FEDEX overnight shipping which came to $53.

Ralph
Feb 19, 2007, 04:10 PM
Plantraco's Avatar
Fantastic Solar Model Ralph! That's a major advancement I'd say!

Maybe we could send you a receiver without the bootup sequence software. Instant -reboot would indeed be better to cope with brownouts. I think for an outdoor model our 900Mhz would have more advantages for that model.

Just like Spirit and Opportunity on Mars, maybe your model can be "Solar Groovy" when the sun is higher up in the sky.

That capacitor idea may work - it just depends on those brownouts.

At 9.5 grams with 4mm drive, it seems like you only have at most 5 grams of thrust. Will the model climb out OK at this weight? (ie: it seems like your propulsion is incredible - maybe it's better at speed or what?).
Feb 19, 2007, 04:38 PM
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Bud:

I'm sure the brown out issue will be forgotten latter in the year when the sun angle gets better here. If not I will contact you about a "solar" version of the receiver. I never had a problem with the larger Sol-Mite (with a JMP Rx.) but it could not fly with the sun where it was yesterday. The micro has a much better power to weight ratio and can fly in less ideal conditions.
I have no way to measure the thrust other than flying. I have found that the Mk4-10 likes a lot of reduction. My scratch built Butterfly using the same watch gears and the 3222 prop does nearly 20 minutes at 6 grams. The solar Mite has a very good climb angle and while I thought thrust would be marginal it flies with authority. With higher sun I should see a bit better thrust even though it does not need it.

Ralph
Feb 20, 2007, 01:20 AM
Plantraco's Avatar
Quote:
Originally Posted by Ralph B
Bud:

I'm sure the brown out issue will be forgotten latter in the year when the sun angle gets better here. If not I will contact you about a "solar" version of the receiver. I never had a problem with the larger Sol-Mite (with a JMP Rx.) but it could not fly with the sun where it was yesterday. The micro has a much better power to weight ratio and can fly in less ideal conditions.
I have no way to measure the thrust other than flying. I have found that the Mk4-10 likes a lot of reduction. My scratch built Butterfly using the same watch gears and the 3222 prop does nearly 20 minutes at 6 grams. The solar Mite has a very good climb angle and while I thought thrust would be marginal it flies with authority. With higher sun I should see a bit better thrust even though it does not need it.

Ralph
Man, that makes me happy to hear that.

So, in theory, you could keep your model aloft for hours and hours on a clear sunny day in summer. It's completely amazing! What a breakthrough!
Feb 20, 2007, 04:41 AM
TheyreComingToTakeMeAway!
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Quote:
Originally Posted by Plantraco
Man, that makes me happy to hear that.

So, in theory, you could keep your model aloft for hours and hours on a clear sunny day in summer. It's completely amazing! What a breakthrough!
or at least until the motor brushes give out

very awsome model Ralph
makes me wonder what those single phase brushless motors could do for solar powered models?
Feb 20, 2007, 07:56 AM

Power required


Ralph,
Congratulations. That is a super achievement.

A little reference about power required to fly:
I have a lightened 'X' Twin (17.6g) which climbs steadily on the minimum power setting, such that I have to switch off to get it down. I have measured the minimum static thrust as 6 grams. This shows that it is possible to fly with the static thrust being only approx. 1/3 the total weight of the model. So in Ralph's model, 3 to 4 grams of thrust could be enough.

John


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